A study on building performance analysis for energy retrofit of existing industrial facilities

Highlights

• Thermal simulation of a historical industrial hall with limited data availability.

• Considering waste heat from machinery after measuring production fluctuations.

• Test of retrofit alternatives for roof and skylights.

• Results indicate a significant reduction in heating energy demand up to 52%.

• After retrofit naturally ventilated hall can achieve thermal comfort in summer.

Abstract

Due to the strengthening of regulations and codes on building energy performance, as well as with the application of national legislations regarding energy management and efficiency, existing industrial facilities are using thermal refurbishment and renovation as impetus for increasing their overall energy efficiency. This paper analyzes a building envelope refurbishment for a case study of an existing historical industrial facility. Critical parameters affecting energy performance of industrial buildings were identified by reviewing relevant literate. Two retrofit scenarios were developed and dynamic thermal simulation using EnergyPlus was implemented to evaluate the potential for improvement. Thereby the impact of interior loads was considered, determined by measurements conducted on factory machines, occupancy and lighting operation patterns. However, information regarding constructions of the existing facility and installed technical building services is limited. There is also uncertainty in the quantification of natural ventilation air change rate for such buildings. To overcome these limitations a study of various material databases was carried out, in order to assess data for building envelope composition. Input values for missing data were provided based on literature, allowing a fair comparison between refurbishment alternatives. Simulation results showed that the heating demand of the facility could be reduced up to 52%, indicating a significant potential for energy savings. Beyond that, thermal performance against summer overheating also depicted considerable improvements as regards to hours exceeding thermal comfort levels.

Introduction

The industrial sector is one of the largest energy consumers reaching 25.6% of the total energy consumption in Europe in 2012 [1]. Apart from the energy used by manufacturing procedures, production facilities also consume considerable amounts of energy for building conditioning. The strengthening of regulations and codes on building energy performance [2], increasing energy costs, as well as the adoption of the ISO 50001 standard on energy management systems by national legislations in order to promote energy efficiency [3], lead existing industrial facilities to use thermal refurbishment and renovation of the building envelope as impetus for improving their overall energy competence.

A leading edge practice in building refurbishments implements dynamic model-based energy simulation tools for estimating energy savings from retrofit alternatives [4], in particular, when this is applied in the early design stages of the process to size the influence of refurbishment measures [5]. Furthermore it should be mentioned that BIM is increasingly used in combination with energy modeling tools [6], serving as knowledge database for necessary information input; an approach also followed in the current research. Potential of BIM use in building refurbishment is reviewed in [7]. Authors state that BIM should be applied from the early stages of a project and that it can assist environmental performance analysis of design alternatives; however solid framework about the process is lacking. Conversion of available data to semantic BIM objects requires high modeling effort and expertise, thus BIM is seldom applied in existing buildings yet [8].

Conducted energy retrofit studies have mainly focused on buildings of the residential [9] and tertiary sector [10]; fields where researchers have achieved significant advancements in developing models and frameworks for identifying the most effective thermal building envelope refurbishment and systems upgrade options. Sophisticated tools have been proposed for thermal optimization and refurbishment of office and commercial buildings. Based on standardized data for such building types, benchmarking values and pre-simulated results a web-based toolkit enables fast calculation of retrofit alternatives and evaluation of multi-criteria parameters like energy and costs savings [11], while another software solution provides information based on a matrix of retrofit measures and economic uncertainty scenarios [12]. Industrial facilities, on the other hand, are seldom studied under an energy retrofit perspective [13], with efforts focusing on thermal envelope when structural upgrades are compulsory [14] or on installed technical building services when these are identified as inefficient, e.g. heating [15], ventilation [16]. Industrial heritage has also been studied under an energy retrofit perspective, however mostly concerning ex-industrial facilities and their transformation to other uses as housing [17], or mixed-use developments [18].

State-of-the-art approach in building refurbishment requires detailed monitoring and in-situ investigation of the pre-renovation state in order to calibrate the simulation models [19] and so enable reliable evaluation of different retrofit alternatives, related to envelope thermal properties [20]. Especially in the case of historical buildings, extensive examination of the building fabric is mandatory as each case is unique and therefore poses challenges in defining a solid model for energy performance assessment [21]. However implementing this approach is not always feasible. When information is lacking, a common alternative is the use of industry standards for construction materials and systems at the time of a building’s construction [22], together with referential values on typical energy performance for buildings of that type. As regards industrial buildings, large-scale building monitoring and measurements necessitate special equipment, resulting in important investments [23]. Data unavailability is also enhanced by the fact that many companies do not track their energy consumption, thus lacking awareness of their energy needs on individual systems [24]. Consequently, the high complexity in terms of energy supply and consumption as well as diverse building typology of industrial facilities makes it difficult to define benchmarks for energy performance comparison.

Even with calibrated building energy models, predicting energy savings with simulation tools has received critique as in many occasions fails to integrate the role of occupants’ behavior as an imponderable factor on the end energy performance [25]. It can be contented that in industrial facilities equipment and machinery are a substitute for this uncertainty factor, as according to Vaghefi industrial loads are often extremely large, non-stationary with random fluctuation over time [26], while thermally contributing to the indoor climate. One of the rare occasions when industrial production process energy consumption benchmark values are provided is in CIBSE Guide F [27]. However the diversity of machinery setups, based on production capabilities and needs, among facilities operating in the same industry branch, makes the use of such referential values in case of industrial building refurbishments inconsistent, as they may not comply to reality. A parametric simulation study about the impact of process loads and occupancy patterns on annual energy demand of a simple hypothetical industrial building observed that the optimum building envelope can differ according to manufacturing conditions, with actual heat emissions, air change rates and daylighting controls having a great influence on the energy performance [28]. Furthermore, on the case of an existing industrial hall in Slovakia, analysis of thermal energy demand and saving potential via measurements, static calculations and dynamic simulations also showed that real interior gains from machinery are crucial for realistic modeling of the building [29]. It is thereby illustrated that thermal simulation of industrial facilities is highly case oriented. Nonetheless, through analyzing research conducted on case studies, parameters affecting energy performance can be identified.

As regards thermal envelope refurbishment, a European research project, including studies on renovation strategies of existing industrial buildings using steel-based technologies, employed thermal simulations and experimental “before and after” measurements (e.g. air tightness tests, wall thermography) to derive empirical relationships for the energy demands of industrial facilities [30]. Results of typical 1960’s/70’s halls in the UK showed that U-value improvement of roof elements had higher impact on the energy demand compared to wall elements and together with upgraded skylights and gutter U-values reduced energy consumption by 49% compared to “before renovation”. Mastrapostoli et al. [31] also pinpointed roof’s significance as cool roof coating essentially decreased summer cooling loads by 73% with a minor heating penalty for an industrial building in the Netherlands.

Moreover, daylight potential of roofs is recognized as regulatory factor of industrial building energy performance. Chen et al. [32] implemented in-field measurements and simulation models on a single floor factory with a hackle-shape roof in China, where daylighting control showed large energy savings in electrical lighting consumption. Wang et al. [33] in the case of a large workshop with skylights, also in China, developed a solution for lighting control based on a sensor network, realizing lighting energy savings of up to an average of 80% on cloudy days. Furthermore, for a light steel structure industrial shed in the UK, complying with local building regulations, researchers studied the influence on energy performance and space overheating when introducing skylights and proposed that unwanted summer solar gains could be remedied by the application of ridge natural ventilation [34]. Brinks et al. [35] indicate that for such light steel constructions, typical for new industrial buildings, summer overheating is a minor problem in Central European climate. This however is depending on machinery internal loads as well as orientation and surface of glazed surfaces.

Taking aforementioned into account, a gap was identified in exploration of thermal refurbishment strategies for existing industrial facilities in operation with actual production process loads. Therefore, this study presents a novel approach to assess the improvement potential on energy consumption and indoor climate of historical industrial halls in operation through application of dynamic thermal simulation modeling. The paper is structured in three more sections. In Section 2 the case study and method for compiling the factory thermal model are thoroughly presented while results of thermal retrofit measures on energy and thermal performance are evaluated in Section 3. Section 4 summarizes the main conclusions and highlights further development needed.